Any ideas to help make the campaign more horror oriented? /hints and tips!

Hey there! I'm a first time DM and had started a home brew campaign for a few sessions before realizing I needed some structure or I was going to fight my players (in game and out of game). I had a grand idea of having my story with some horror aspects, and I was hoping to add some into the witchlight carnival/the witches reign on the feywild. We're about 2 sessions in to the actual carnival, and they've found Rubin in the Hall of Mirrors, talked to Candlefoot, began hunting down Kettlesteam, and participated in the cupcake eating and pixie kingdom. They've been a bit bad about keeping the mood up in the carnival, but I don't want that to keep them from experiencing the carnival, I just want to put a horror twist on it, while they try to get the mood back up or fight through it to get to the owners. I feel as though cutting the carnival short and having the owners come directly to them can leave some super fun mechanics out. I've already given them some horror aspects, as I had sowpig, after running off away from rubin in the mirror, follow them from mirror to mirror until they found their way out. Let me know if y'all have done anything similar/have resources that would help! Again, first time DM, long time player, so any help is so so so appreciated!!